[Radiance-general] Objects with plastic material in IBL scene

[Greg Ward]

Giulio is correct.  IBL creates glow sources rather than lights, so  
materials with primarily diffuse components rely on the ambient  
calculation to pick up any illumination at all, and the parameters must  
be set such that Radiance can find the bright areas in the light probe.  
  Something like -ab 1 -ad 1024 -as 512 at least, and sometimes even  
that is not enough.  There are tools for locating and replacing bright  
areas in the light probe with equivalent sources.  I think HDRshop has  
such a tool, and others have worked on similar tools.  There are even a  
number of papers on it -- I know Alex Keller wrote one, and Bernhard  
Spanglang worked on this as part of his thesis, and you can check out  
his talk from the first Radiance workshop online:

	http://www.radiance-online.org/radiance-workshop1/cd/Spanlang/ 
index.html

See also Santiago Torres' presentation from the second workshop:

	http://www.radiance-online.org/radiance-workshop2/cd/Torres/ 
abstract.html

This topic is also well-covered in the notes Paul Debevec has online at  
his website from the various Siggraph tutorials he's given.  See for  
example page 8 from "Paul Debevec's main slides on HDRI and Image-Based  
Lighting (6.7MB pdf)" in the notes of the Siggraph 2003 course on IBL:

	http://www.debevec.org/IBL2003/

There are resources out there.  It's a matter of finding them, as  
always...

-Greg

> From: Giulio Antonutto <Giulio.Antonutto at arup.com>
> Date: March 2, 2005 6:54:23 AM PST
>
> A possible reason:
>
> is it -ab > 0 (i.e. rvu -ab 1 or rpict -ab 1) ?
> (needed if there are only secondary sources of light, such as the  
> Sky...)
> hope it helps,
> giulio
>
> PS I have Radiance 3.6.1 on 10.3.8, MacOSX, everything ok here, BTW  
> it's a
> pleasure to see how many people are running Radiance on a Mac ;-))
>
> -----Original Message-----
> From: radiance-general-bounces at radiance-online.org
> [mailto:radiance-general-bounces at radiance-online.org] On Behalf Of Kirk
> Thibault
>
> I had this occur as well when previewing in rview (rvu) but everything
> rendered fine when a final render was made.
> To answer your question, I don;t know why.  I run RADIANCE on a Mac,
> OSX 10.3.X.
>
> kirk
>
> On Mar 2, 2005, at 5:13 AM, Tarik Rahman wrote:
>
>> Hi
>> Does anyone know why inserting a diffuse object in an IBL scene, such
>> as the
>> red_plastic sphere in the Debevec tutorial does not reflect light
>> properly,
>> i.e. renders as black? It works sometimes and other times it doesn't,
>> I don't
>> understand why. The metal spheres such as the gold and steel ones and
>> the
>> crystal  sphere all render perfectly but sometimes (not all the time)
>> any
>> object with plastic material doesn't render properly.
>>
>> Tarik